1. Field of the Invention
This invention relates to an agricultural mulch and a method of depositing the mulch on a growing field in a manner to extend the longevity of the mulch and protect the mulch against premature degradation and removal from the field.
2. Description of Background Art
Agricultural mulch films are used extensively throughout the world because of the many advantages they provide, including fertilizer retention, fumigant retention, retarded weed growth, increased soil retention of moisture and heat, and reduced soil erosion by winds and rain. Such mulching films also enhance soil structure by preventing soil crusting and soil compaction.
Polyethylene film both in a transparent state and an opaque state, has been the most common synthetic mulch to be used. However, polyethylene film is not degradable and it must be removed from the field and be burned, buried or otherwise discarded at the end of its useful life. The removal and burying or burning of plastic mulch is both costly and has an adverse effect on the ecology. There exists a need for a mulch that would decompose at the end of a growing season. Attempts to meet this need have led to the development of a variety of biodegradable and photodegradable mulch films. For example, Otey et al. U.S. Pat. No. 3,949,145 developed a biodegradable plastic film from starch, polyvinyl alcohol and glycerol, which film is covered with a water-resistant resin coating to prevent premature degradation. The water-resistant resin coating is prepared from a water-resistant resin, such as plasticized polyvinyl chloride, and poly-toluene diisocyanate prepolymer bonding agent.
Another biodegradable mulch film, disclosed by Clendinning, U.S. Pat. No. 3,929,937, is fabricated from a blend of a particulate addition polymer, such as polyethylene, in a matrix of biodegradable thermoplastic oxyalkanoyl polymer, such as .epsilon.-caprolactone homopolymer. Additional ingredients can be included in the blends. Such additional ingredients include naturally occurring biodegradable products, e.g., tree bark, sawdust, peat moss, cotton seed hulls, and the like, fibrous and non-fibrous fillers, e.g., talc, limestone, bentonite, asbestos, and the like, plant nutrients, fertilizers, insecticides, pesticides, and the like.
In Iwasyk et al., U.S. Pat. No. 3,387,405, there is disclosed a continuous foam mulch which is produced by applying and substantially simultaneously gelling a fluid aqueous foam which comprises at least 0.5 weight percent of dissolved polyvinyl alcohol and at least 50 percent, based on the weight of the polyvinyl alcohol, of emulsified asphalt or wax.
Still other agricultural mulch films have been disclosed by Vigneault et al., U.S. Pat. No. 3,274,731, and Kane, U.S. Pat. No. 3,384,993. Vigneault et al., for example, discloses a mulch film comprised of at least one copolymer consisting essentially of ethylene and an ethylenically unsaturated carboxylic acid monomer such as acrylic acid, methacrylic acid, fumaric acid, maleic acid and the like. Vigneault et al. suggests that their films might also contain nutrients such as ammonia or phosphate-containing additives, and other filler for various mulching uses. Kane also discloses a plastic mulch film that may include solid water-soluble nutrients such as ammonium nitrate, potassium chloride, potassium nitrate, potassium sulfate and urea. However, the only plastic mulch films disclosed by Kane are comprised of polyethylene, polypropylene, cellulose acetate, cellulose acetate butyrate, polyvinyl chloride acetate, styrene acrylonitrile, and the like. These plastic materials are not soluble in water and must, therefore, rely on some other mechanism to impart adequate degradability so that they may be used as an agricultural mulch film that does not have to be removed from the fields after the growing season.
One such degrading mechanism is disclosed by Newland et al., U.S. Pat. No. 3,545,510. In that patent, it is taught to include a prooxidant in a water-insoluble polyolefin film, such as polyethylene, polypropylene or poly(butene-1). Among the pro-oxidants that are disclosed are certain metal acetyl acetonates, metal alkyl benzoylacetates, metal acetyl acetonates, metal stearates and metal oleates.
Alternatives to plastic mulching films have also included paper strip material for sowing seeds. Soviet Patent, SU 1209059A disclosed a paper strip material such as blotting paper to which seeds and fertilizers are applied. The outer surface of the strip material has a coating of herbicide. Seeds are sandwiched between two strips glued together. Another tube-like paper seed strip is disclosed in U.S. Pat. No. 3,623,266.
Japanese Application No. A-59-169992, assigned to Nissan discloses fertilizer sheet production by spreading granules of slow action fertilizer over base paper coated with an adhesive. Japanese Patent #60025902, Feb. 2, 1985 assigned to Dainippon Jochugiku KK discloses an insecticidal paper which comprises paper coated with printing ink and binder containing volatile insecticide which is overcoated with a resin film. Coating used include nitrocellulose, polyamide, ethyl cellulose, acrylate resins, vinyl chloride-vinyl acetate copolymers, and urethane resins.
Japanese Patent #8647900, Mar. 8, 1986 assigned to Oji Paper Co., Ltd. discloses a moisture impermeable controlled release insecticidal sheet. The sheets are made from kraft paper, rubber latex and waxes or waxy substances, and insecticides, fungicides and fungistat.
British Patent No. 1,434,042, discloses a water-soluble or water-dispersible paper made from polyvinyl alcohol on which or into which an active ingredient is incorporated.
U.S. Pat. No. 5,163,247 to Weber et al. discloses a porous fibrous cellulosic web at least partially saturated with latex at 30 dry parts per 100 parts fiber.
While the above-discussed mulch films, and others, have been used with some degree of success, no mulching film disclosed to date has been found to be completely satisfactory commercially in the balance of the important properties needed for a good agricultural mulch. These properties include, for example, good mechanical properties for application by machines and planting by machines, water resistance, field durability, the ability to retard weed growth, degradability and appropriate economics.
The agricultural mulch according to the invention is a special configuration of a mulch having a paper extensible substrate in which the mulch is disposed along the furrows of a growing field in a particular manner. The mulch itself may be coated on its top and bottom surfaces as described in the copending U.S. application Ser. No. 08/660,894 claiming benefit under 35 U.S.C. 119(e) to application Ser. No. 60/002,092 filed Aug. 10, 1995 as a provisional application per 35 U.S.C. 111(b).
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.